I tried turning my bass over to check your idea. I only saw a faint glow, only when turning the bass out some at the bottom. I installed my kit flush with the bottom of the fretboard on the traditional side (as opposed to flush with the top) to make sure it didn't interfere with my rudimentary playing. Although the picture on the website suggests a raised array, it really is quite low and unobtrusive. SO... I don't think you would find a bottom array satisfactory. You might want t consider Sims for a front-facing array as Mr. King has.
 
Larry

Sounds like you should order a bass with front LEDs!

I do have basses with front LEDs and since the LEDs are centered they're still not the same as if they'd be located closer to the rim. Yet, I don't like the looks of the displaced front LEDs ? la King Bass, so this is not an option. In any case it was just fooling with an idea. I am sure I can still live with the regular side LEDs solution. Thanks for your test, Larry!  
 
While this would be for a fretless anyways I have already checked with SIMs for the option of illuminated fret lines, but it would be expensive! Also, I would prefer to keep the neck unlined.  
 
As I said, it was just fooling around with different ideas. No problem if they turn out to be bad ideas ...

Perhaps a miner's helmet...that's probably one of the bad ideas, huh?!
 
Larry

Yeah, probably , along with products such as Fretlaser: http://www.fretlord.com/Fretlaser.htm
 
Odd...